1. Field of the Invention
The invention is directed to shorting switches and, in particular, to shorting switches for eliminating arcing faults in power distribution equipment. The invention is also directed to shorting systems for eliminating arcing faults in power distribution equipment.
2. Background Information
There is the potential for an arcing fault to occur across the power bus of a motor control center (MCC), another low voltage (LV) or medium voltage (MV) enclosure (e.g., a LV or MV circuit breaker panel) and other industrial enclosures containing LV or MV power distribution components. This is especially true when maintenance is performed on or about live power circuits. Frequently, a worker inadvertently shorts out the power bus, thereby creating an arcing fault inside the enclosure. The resulting arc blast creates an extreme hazard and could cause injury or even death. This problem is exacerbated by the fact that the enclosure doors are typically open for maintenance.
A high-speed shorting switch is needed for low and medium voltages as an alternative to arc proofing switchgear enclosures. Presently, manufacturers are developing more robust enclosures, which contain and direct the hot gases and flames out the top of the enclosure upon the occurrence of an internal arcing fault (e.g., a short across the bus bar, breaker, cable phase-to-phase or phase-to-ground). These faults can occur from a wide variety of sources, such as, for example, animals that crawl into the enclosure, tools left behind from maintenance crews, insulation failure, earthquakes, and other mechanical damage.
Rather than trying to contain and direct the blast, a new idea has been developed by others for eliminating the arcing fault altogether. This is done by shorting out the power bus either phase-to-phase or phase-to-ground. Known shorting switches use a variety of closing and holding techniques which are very expensive to buy and to maintain. Such switches are located on the main power bus to shut down the entire power bus system when a fault occurs even if the fault is only on the load side of a branch circuit.
It is known to employ various types of crowbar switches for this purpose. The switches short the line voltage on the power bus, eliminating the arc and preventing damage. The resulting short on the power bus causes an upstream circuit breaker to clear the fault.
Examples of medium voltage devices include a stored energy mechanism with vacuum interrupter contacts, and a mechanism to crush a conductor magnetically.
An example of a low voltage device is a stored energy air bag actuator, which drives a conductive member having a pin and a flange, in order to short two contacts. The first contact is in the form of a receptor for capturing the pin of the driven conductive member. The second contact has an opening, which allows the pin to pass therethrough, but which captures the flange of the driven member.
There is room for improvement in shorting switches and systems that respond to arcing faults and switch fast enough in order to protect workers and equipment from arc blasts associated with power distribution equipment.
These needs and others are met by the present invention, which provides a magnetically actuated high-speed shorting switch suitable for low or medium voltage switchgear applications.
As one aspect of the invention, a shorting switch for eliminating arcing faults in power distribution equipment comprises: a magnetic core having a pin member and an opening; a first terminal; a second terminal; a conductor electrically connected between the first and second terminals, the conductor passing through the opening of the magnetic core; a switch member pivotally mounted to the pin member of the magnetic core and adapted to pivot toward and engage the conductor in response to arcing fault current flowing through the conductor; a third terminal, which is electrically interconnected with the switch member; a latch member having a first position, which holds the switch member apart from the conductor, and a second position, which releases the switch member to permit the switch member to pivot toward the magnetic core and engage the conductor in response to the arcing fault current; and means for unlatching the latch member in response to an activation signal.
The latch member may have a first end, which engages the switch member, a pivot point, and a second end. The means for unlatching the latch member in response to an activation signal may include a solenoid having a plunger, which moves the second end of the latch member to pivot the latch member about the pivot point and cause the first end of the latch member to release the switch member.
The magnetic core may have a surface, and the switch member may be adapted to pivot toward the surface of the magnetic core. The switch member surface may be normally disposed at an arcuate angle with respect to the surface of the magnetic core.
As another aspect of the invention, a shorting switch for eliminating arcing faults in power distribution equipment comprises: a magnetic core having a pin member and an opening; a first terminal; a second terminal; a conductor electrically connected between the first and second terminals, the conductor passing through the opening of the magnetic core; a switch member pivotally mounted to the pin member of the magnetic core and adapted to pivot toward and engage the conductor in response to arcing fault current flowing through the conductor; a third terminal, which is electrically interconnected with the switch member; a latch member having a first position, which holds the switch member apart from the conductor, and a second position, which releases the switch member to permit the switch member to pivot toward the magnetic core and engage the conductor in response to the arcing fault current; a vacuum bottle, with the conductor, the magnetic core, the pin member, and the switch member being disposed within the vacuum bottle; and means for unlatching the latch member in response to an activation signal.
The first, second and third terminals may be disposed outside the vacuum bottle. The switch member may have a first end disposed within the vacuum bottle and a second end disposed outside the vacuum bottle. The first and second terminals may be adapted for operation with medium voltage power distribution equipment.
As another aspect of the invention, a shorting system for eliminating arcing faults in power distribution equipment comprises: a magnetic core having a pin member and an opening; a first terminal; a second terminal; a conductor electrically connected between the first and second terminals, the conductor passing through the opening of the magnetic core; a switch member pivotally mounted to the pin member of the magnetic core and adapted to pivot toward and engage the conductor in response to arcing fault current flowing through the conductor; a third terminal, which is electrically interconnected with the switch member; a latch member having a first position, which holds the switch member apart from the conductor, and a second position, which releases the switch member to permit the switch member to pivot toward the magnetic core and engage the conductor in response to the arcing fault current; means for unlatching the latch member in response to an activation signal; and means for detecting an arcing fault and responsively outputting the activation signal.
The second terminal may be adapted for electrical connection upstream of a plurality of circuit breakers. The first terminal may be structured for electrical connection with a load terminal of a single circuit breaker.